1. Field of Invention
The present invention relates to a process for purifying and recycling printing and dyeing wastewater, and more particularly to a purifying and recycling process for deeply treating printing and dyeing wastewater based on a combination of nanometer catalytic microelectrolysis technology and membrane technology.
2. Description of Related Arts
Textile industry generally includes spinning, printing and dyeing, chemical fiber, clothing and manufacture of textile devices. With the fast development of the economy, the printing and dyeing industry also enters a fast developing period, the devices and technology are improved obviously, the production process and devices are changed continuously, and the printing and dyeing companies develop very fast. So far, there are more than 2,000 printing and dyeing companies above designated size in China. The printing and dyeing processes refer to physical and chemical process to various textile material fibers, yarns, and cloths in production, and include pre-treating, dyeing, printing, and after-treating of textile materials which are together called printing and dyeing processes. At present, the development of the textile technology is guided with ecological fabrics production and green production technology, catches the source through multi-channels including processes, adjuvants, and devices, emphasizes the ecological problems of each link, optimizes the textile processes hard, and reduces the consumption of chemical agents, water and energy, so as to achieve the goal of high efficiency, high speed and environment-friendliness. A great effort is paid to environment-friendly dye stuff adjuvants, new processes saving water, energy and reducing emission and new devices at home and abroad, and an obvious progress is made in printing and dyeing technology with no water or less water, printing and dyeing of painting, and utility model of textile saving energy and water. However, despite the fast development of the technology of saving water and treating wastewater in the textile printing and dyeing industry, the textile printing and dyeing wastewater is still an important pollution source in China's industrial system. According to the statistics of Ministry of Environmental Protection of the People's Republic of China, the printing and dyeing wastewater drained by the printing and dyeing industry is the fifth largest in all the industrial departments of China. The character of the printing and dyeing wastewater as an important environment pollution source is firstly large amount. At present, the printing and dyeing products are about 800,000˜900,000 tons in the world, and China has 150,000 tons, ranking in the top. About 10%˜15% of the printing and dyeing components are drained into the environment along with wastewater in production and use of the printing and dyeing products. The printing and dyeing industry and textile printing and dyeing industry are high developed, and the printing and dyeing wastewater pollutes the environment more seriously. In 2004, the printing and dyeing industry drained 1.36 billions m3, and the pollutant is the sixth largest in all the industrial departments calculated by COD. Secondly, the type of printing and dyeing components as environmental pollutants have many species and complex structures. The synthesis printing and dyeing components have more than 30,000 species, and more than 80% of them contain complex organic compounds of azo bond and poly-aromatic. Printing and dyeing industry is one of the industries of extremely serious environmental pollution in the chemical industries. The printing and dyeing wastewater has large chromaticity, high concentration of organic matters, complex components, many hardly biodegradable substances, and contains a large number of inorganic salts, sulfides, etc., are intractable industrial wastewater. The printing and dyeing components are hard to be removed due to its complex aromatic hydrocarbons molecular structure, which are desired to exist stably in water environment or under illumination and oxidants when designing and production. Thirdly, most printing and dyeing components are toxic non-degradable organic matters having strong chemical stabilization, and carcinogenic, teratogenic and mutagenic effects. Even the concentration of the remained printing and dyeing components are low in the wastewater, it will also reduce the light transmittance of water body after draining into the water body, so as to cause damage to the water ecological system. Therefore, efficiently treating the printing and dyeing wastewater has become an important problem.
The printing and dyeing wastewater has characters such as high concentration and large number of species of pollutants, containing toxic and harmful components and high chromaticity. The ordinary treating methods to the printing and dyeing wastewater at home and abroad comprise physical methods, chemical methods, biological methods, and etc.
1. Physical Methods
The physical methods mainly comprise flotation method of adsorption, membrane separation method, ultrasonic gas vibration method, and distillation method. The adsorption method is applied mostly in the physical methods. At present, the activated carbon adsorption method is mainly adopted in international. The method is very effective for removal of dissolved organic matters, but can not remove colloids and hydrophobic dyeing, and has good adsorption properties to the water-soluble printing and dyeing components in cationic printing and dyeing, direct printing and dyeing, acid printing and dyeing, reactive printing and dyeing.
Adsorption flotation method first absorbs printing and dyeing ion and other soluble substances from the wastewater with highly dispersed powdery inorganic adsorbents such as bentonite and kaolin, then adds the flotation agent to obtain hydrophobic particles by airfloating, the removal efficiency of acid printing and dyeing, cationic printing and dyeing, and direct printing and dyeing can be more than 92%.
The membrane technology applied in treating printing and dyeing wastewater mainly comprises ultra-filtraten and reverse osmosis. The ultra-filtraten technology has a decolourization rate of 80%˜97%, and a TOC removal rate of 60%˜85% in treating scattered printing and dyeing wastewater. The reverse osmosis technology has a removal rate of soluble solid of 85%˜-99%, and an average recycle rate of 75%˜85%.
The ultrasonic technology can become an effective method of treating wastewater by controlling the ultrasonic frequency and saturation of gas. The Zhangjiagang Jiuzhou Fine Chemical Industry treats printing and dyeing wastewater with the FBZ wastewater treatment equipment designed according to ultrasonic gas vibration technology, and has an average chroma removal rate of 97%, a CODCr removal rate of 90.6%, and a total pollution load reduction rate of 85.9%.
2. Chemical Methods
Chemical methods mainly comprise chemical coagulation method, chemical oxidation method, photochemical catalytic oxidation method, and electrochemical method. The chemical coagulation method is a frequently used method of treating printing and dyeing wastewater, and was thought to be one of the most efficient and economic decoloring technologies. The chemical oxidation method is a main method of decoloring printing and dyeing wastewater, decolors by destroying printing and dyeing color groups with various oxidation methods. Depending on the oxidants and oxidation condition, the chemical oxidation method is divided into ozone oxidation method and deep oxidation method. Furthermore, the photochemical catalytic oxidation method as a deep oxidation technology for reducing organic matters develops fast in recent years. Referring to ZHANG Gui-Ian, Photodegradation of dyes in water using rotation reactor [J]. JOURNAL OF TEXTILE RESEARCH, 2005, 26(3): 109-111, the photochemical catalytic oxidation method achieves good decoloring effect in degrading printing and dyeing wastewater. The electrochemical method purifies printing and dyeing wastewater by electrode reaction.
Microelectrolysis method is an electrochemical technology using iron and carbon filler corroded in the electrolyte solution to form numerous tiny primary cells to treat wastewater. It is a wastewater treating method combining electrolysis, coagulation, electrolytic flocculation, adsorption and other physical and chemical effects in one. In the treatment of printing and dyeing wastewater, printing and dyeing molecules are first adsorbed onto the carbon surface, and have oxidation or reduction reactions in the two poles. The electrode can also be used for electrolysis. Referring to Jia Jinping, Shen Zhemin, Wang Wenhua, The Status Quo and Progress on Treating Methods of Wastewater Containing Dyestaff, 2000, 191:26-29, the integrated performance of electrode conductivity, adsorption, catalytic, redox, the flotation of activated carbon fiber electrode is used to achieve a one-stop process of adsorption—electrode reaction—flocculation and desorption, and the decolorization rate is 98%, CODCr removal rate is greater than 80%. Referring to YAN Bin, FU Hai-yan, CHAI Tian, JIN Lei, SHI Qian, Application of Microelectrolysis Method in Dyehouse Wastewater Treatment, JOURNAL OF XIAMEN UNIVERSITY OF TECHNOLOGY, 2008, 16(1):18-22, decoloring and CODCr removal effects to wastewater produced by cotton series and chemical fiber synthetic woven fabrics with microelectrolysis technology of iron—carbon electrode is studied, when the mass ratio of iron to carbon is 2:1, HRT is 1.5 h, the COD removal rate is up to 55%, chromaticity removal rate is 95%, BOD/COD increased from 0.3 to 0.5. Referring to Luo Jingsheng, Zeng Kangmei, Zuo Jingying, Li Xin, Liu Fude, TREATMENT OF DYE WASTEWATER BY MICROELECTROLYSIS PROCESS, TECHNOLOGY OF WATER TREATMENT, 2005, 31(11):67-70, treating production wastewater containing dyestuff, dye intermediate, and adjuvant with circulating iron—carbon microelectrolysis method is studied. The result shows that pH of the raw water has great affect to treating effect. When pH is within 1˜5, the lower pH is, the better the treating effect is, and when pH is 1, COD removal rate is about 60%, chromaticity removal rate is above 94%. Referring to Deng Xihong, Wang Chao, An Engineering Example of Treating Dyeing Wasterwater Using Microelectrolysis—Physical and Chemical—Biochemical Method, Environmental Science and Management, 2008, 33(3):120-122, the printing and dyeing wastewater of high pollutant concentration, large concentration fluctuations, alkaline, high chromaticity, and biorefractory property is treated with Microelectrolysis—Physical and Chemical—Biochemical Method, which runs continuously for three months, and the result shows that the method runs stably, has low investment and low treating cost, (0.765 RMB per ton), the removal rates of COD, BOD, SS and chromaticity are respectively above 94%, 96%, 89%, and 96%. The indexes of effluent quality all meet emission standards. EpolitoW illiam J,HanbaeYang, et al. studies microelectrolysis to RB4 (Reactive Blue4) wastewater. The experimental result shows that the decoloring rate gradually increases with the decreasing of pH, and increasing of stirring, experimental temperature and ionic strength. There are also many other reports about treating printing and dyeing wastewater with electrochemical method.
3. Biochemical Methods
The printing and dyeing wastewater is biorefractory, so if desiring treating with biochemical methods, MLSS of the activated sludge can be increased, and biochemical performance of the activated sludge can be improved, or efficient strains are used to increase biochemical effect. Breeding and training excellent decolorization flora is an important development direction of the biochemical methods. The research of formation of engineering bacteria with multiple plasmids efficiently decoloring printing and dyeing wastewater by use of mutation breeding, protoplast fusion, and genetic engineering techniques. The recent studies show that the dominant bacteria of the Pseudomonas bacteria, Sphaerotilus natans, Arthrobacter, Bacillus subtilis, and oxidative yeast have a considerable effect of in degradation of printing and dyeing wastewater.
In recent years, the combination of chemical and physical methods for treating printing and dyeing wastewater, or the combination of biological treatment and physical treatment for printing and dyeing wastewater has developed rapidly. Chinese patent of ZL 200710008643.0 discloses a treating method for printing and dyeing wastewater based on membrane technology, which combines chemical coagulation and sedimentation, biological treatment, and reverse osmosis separation technology for treating combines printing and dyeing wastewater.
Although the above methods all have good treating effect, the following problems still exist.
In the physical and chemical aspect, activated carbon has good adsorption effect, but activated carbon is difficult to regenerate, has high cost, and thus its application is limited. Many companies turn to other adsorbent of cheaper and easy-to-get materials. Electrolysis method and oxidation method has certain effect in removing chromaticity of printing and dyeing wastewater, but COD removal is often not satisfactory, the cost of the treatment agents is relatively high. Many new means of oxidation are still in the research phase, and have not being industrialized.
In biochemical aspect, printing and dyeing products are typical fine chemical products, with characteristics of small volume and numerous varieties, and its structure is complex, production process is long, operations of nitration, condensation, reduction, oxidation, diazotization, and coupling are often accompanied from raw materials to finished products. By-products are many, production yield is low, wastewater has complex organic composition, chemical reaction of printing and dyeing production, and processes of separation, refining, and washing all use water as solvent, and thus water consumption is large. Biochemical treatment of printing and dyeing wastewater has the advantages of less investment, but there are still disadvantages that micro-organisms are difficult to adapt to printing and dyeing wastewater, water quality is volatile, and toxicity is big. And problems of sludge disposal, anaerobic biogas processing and complex management also exist. In addition, although the iron-carbon microelectrolysis electrode made some progress in the treatment of printing and dyeing wastewater, the consumption of iron-carbon produces a lot of precipitation, so that treated wastewater is difficult to use, only to meet emission standards.
The treatment of printing and dyeing wastewater using a single method is often difficult to achieve the desired results. The conventional method is to combines each treating methods, which has drawbacks of long process, high operating cost, and unstable water quality. The treated wastewater ordinarily reaches to the emission standard II. The discharged wastewater are processed with a variety of methods of biochemical, chemical, and physical and chemical treatment, so the physical and chemical properties are very stable, any following decolorizing purification becomes very difficult, and general methods are difficult to further decolor or purify the wastewater. The deeply treated wastewater reaching emission standard II will have long-term impact on the environment. On the other hand, the current fresh water resources are increasingly lacking, and water supply has become increasing problem. If deeply treated printing and dyeing wastewater can be reused as recycled water, it will not only significantly reduce the impact on the environment, but also save a lot of fresh water resources.